\(cos^215^o+cos^225^o+cos^235^o+cos^245^o+cos^255^o+cos^265^o+cos^275^o\)

=\(sin^275^o+sin^265^o+sin^255^o+cos^245^o+cos^255^o+cos^265^o+cos^275^o\)

=1+1+1+\(\dfrac{1}{2}\)=\(\dfrac{7}{2}\)

d)  c o s 2 25 0 - c o s 2 35 0 + c o s 2 45 0 - c o s 2 55 0 + c o s 2 65 0

= c o s 2 25 0 - c o s 2 35 0 + c o s 2 45 0 - sin 2 35 0 + sin 2 25 0

= cos 2 25 0 + sin 2 25 0 - cos 2 35 0 + sin 2 35 0 + c o s 2 45 0  

= 1 - 1 + 1/2

= 1/2

Ảnh hiển thị bị lỗi hết rồi bạn. Bạn coi lại.

a) ĐKXĐ: x≠ \(\dfrac{1}{2}\); x≠ \(\dfrac{-1}{2}\); x≠0

    A= \(\left(\dfrac{1}{2x-1}+\dfrac{3}{1-4x^2}-\dfrac{2}{2x+1}\right):\dfrac{x^2}{2x^2+x}\)

       = \(\left(\dfrac{2x+1-3-2\left(2x-1\right)}{4x^2-1}\right):\dfrac{x^2}{2x^2+x}\)

       =  \(\left(\dfrac{2x+1-3-4x+2}{4x^2-1}\right):\dfrac{x^2}{2x^2+x}\)

       = \(\dfrac{-4x}{\left(2x+1\right)\left(2x-1\right)}.\dfrac{x\left(2x+1\right)}{x^2}\)

       =  \(\dfrac{-4x^2}{x^2\left(2x-1\right)}\)

       = \(\dfrac{-4}{2x-1}\)

b) Tại x= -2 ta có A= \(\dfrac{-4}{2.\left(-2\right)-1}\)= \(\dfrac{4}{5}\)

c)  A= 4 ta có \(\dfrac{-4}{2x-1}\)=4

                  ⇔ -4 = 4(2x-1)

                  ⇔ -4 = 8x-4 

                   ⇔ x = 0

d)  A=1 ta có \(\dfrac{-4}{2x-1}\)=1

                   ⇔  -4 = 2x-1

                    ⇔ x= \(\dfrac{-3}{2}\)

là A nhé 1 giá trị

D

D

D

A

   B. Tính trung bình cộng.

A